The invention concerns an arrangement for a slipring-free measurement of the current flowing in the conductors of the rotor component of an electric machine, especially the rotor current of an a.c. exciter with external poles for the excitation of a synchronous machine energized by way of rotating rectifier elements, with a sending unit in the rotating part and a receiving unit in the stationary part of the machine. Such an arrangement is known, for example, in view of published German application DT-AS 1 080 221.
Arrangements of this type are needed to measure the excitation current of brushless synchronous machines. Since the excitation current is generated in a rotating armature of an a.c. exciter, it would either be necessary to transfer, for the purpose of measurement, the excitation current by way of slip-rings from the rotating part of the machine to the stationary part and then to return it, or to produce across a resistor a voltage drop that is proportional to the current and to transfer this measured value by way of slip-rings to the stationary part. A relatively accurate measurement of the excitation current is needed, for example, in order to determine the temperature rise within the excitation winding.
However, the use of slip-rings in measuring circuits not only causes measuring errors but is also undesirable because of the required service maintenance. The above mentioned known arrangement provides at the rotating body of the exciter armature an additional magnetic system through which flows the excitation current generated within the exciter armature and which is faced by an additional, stationary winding where a voltage is induced that is proportional to the current flowing through the rotating magnetic system. However, the additional magnetic system and the additional stationary winding will increase the axial dimensions of the exciter and thus the overall length of the turboset, leading to a -- practically always disadvantageous -- lowering of the critical bending speed, and increasing also the construction costs, for example, for the power station building.